Process for preparing a phenylalanine derivative and intermediates thereof

ABSTRACT

The present invention provides a process for preparing a novel phenylalanine derivative of the formula (1): wherein X1 is a halogen atom, X2 is a halogen atom, Q is a group of the formula —CH2— or —(CH2)2— and Y is a lower alkyl group, or a pharmaceutically acceptable salt thereof, which has excellent inhibitory effects on α4 integrin-mediated cell adhesion, and an intermediate useful in the process.

TECHNICAL FIELD

The present invention relates to a novel process for preparing novelphenylalanine derivatives. The present invention also relates to novelcompounds useful as intermediates of the process.

BACKGROUND ART

Integrins participate in various in vivo functions through the bindingto adhesion molecules classified into immunoglobulin super family,sialomucin family, and the like. Integrins are composed of subunitsreferred to as alpha (α) and beta (β) subunits, and there have beenidentified sixteen α subunits and eight β subunits so far. The α₄subunit associates with the α or 7 subunit, and forms α₄β₁ and α₄β₇integrins, respectively, which are hereinafter referred to as “α₄integrin” collectively.

It is known that α₄ integrin is involved in various diseases through theadhesion to mucosal addressin cell adhesion molecule-1 (MAdCAM-1),vascular cell adhesion molecule-1 (VCAM-1) or connecting segment 1(CS-1) on fibronectin. It is also known that when adhesion of α₄integrin is inhibited by an anti-α₄ integrin antibody, the symptoms ofallergic bronchitis, inflammatory bowel disease, rheumatoid arthritis,experimental autoimmune encephalomyelitis, and the like are alleviated.

It has been reported that there are compounds capable of inhibiting α₄integrin-mediated cell adhesion and that they are useful in treatment ofdiseases related to α₄ integrin-mediated cell adhesion (see, WO 01/12183and WO99/36393). However, those publications do not disclose compoundshaving a lower alkoxy-C₁₋₂ alkyl group at the 4′-position ofbiphenylalanine nucleus, and a process for preparing the same.

DISCLOSURE OF INVENTION

One of objects of the present invention is to provide a novel processfor preparing a phenylalanine derivative of the formula (I):

wherein X¹ is a halogen atom, X² is a halogen atom, Q is a group of theformula —CH₂— or —(CH₂)₂— and Y is a lower alkyl group, or apharmaceutically acceptable salt thereof, which has excellent inhibitoryactivity against α₄ integrin-mediated cell adhesion.

Thus, the present invention relates to a process for preparing acompound of the formula (I):

wherein the symbols are the same as defined above, or a pharmaceuticallyacceptable salt thereof, comprising

-   (1) coupling a compound of the formula (VI):    wherein Z is a leaving group, R¹NH is a protected amino group and    CO₂R is a protected carboxyl group with a compound of the formula    (V):    wherein the symbols are the same as defined above, removing the    protecting group from the protected amino group, and if necessary,    converting the resulting compound into a salt, to yield a compound    of the formula (IV):    wherein the symbols are the same as defined above, or a salt    thereof,-   (2) condensing the compound (IV) or a salt thereof with a compound    of the formula (III):    wherein the symbols are the same as defined above, a salt or a    reactive derivative thereof to yield a compound of the formula (II):    wherein the symbols are the same as defined above, and-   (3) removing the protecting group from the protected carboxyl group    of the compound (II), and if necessary, converting the resulting    compound into a pharmaceutically acceptable salt.

BEST MODE FOR CARRYING OUT THE INVENTION

The process of the present invention will hereinafter be explained inmore detail.

The compounds used in the process of the present invention may be in theform of a salt so long as the reactions are not adversely affected.Examples of the salt include a salt with an inorganic acid such ashydrochloric acid, hydrobromic acid, sulfuric acid, nitric acid orphosphoric acid; a salt with an organic acid such as acetic acid,tartaric acid, citric acid, fumaric acid, maleic acid, toluenesulfonicacid or methanesulfonic acid; a salt with a metal such as sodium,potassium, calcium or alminium; and a salt with a base such asethylamine, guanidine, ammonium, hydrazine, quinine or cinchonine. Whenthe compounds used in the reactions are available in the free form, theycan be converted into a salt in a conventional manner, and vice versa.

(1) STEP 1:

The coupling reaction of compound (VI) with compound (V) can be carriedout in a suitable solvent in the presence of a catalyst and a base.

The protecting group for the amino group of compound (VI) can beselected from the amino protecting groups that can be removed easilyunder conventional conditions. Examples of such amino protecting groupsinclude a substituted or unsubstituted aryl-lower alkoxycarbonyl groups(e.g., benzyloxycarbonyl group and p-nitrobenzyloxycarbonyl group), alower alkoxycarbonyl group (e.g., t-butoxycarbonyl group),9-fluorenylmethoxycarbonyl group, etc. Above all, a lower alkoxycarbonylgroup is preferred and t-butoxycarbonyl group is most preferred.

Examples of the protected carboxyl group of compound (VI) includeesterified carboxyl groups. Specific and preferred examples of theesterified carboxyl groups include carboxyl group esterified with alower alkyl group, a lower alkenyl group, a lower alkynyl group, an aryllower alkyl group (e.g., benzyl group), an aryl group (e.g., phenylgroup), and the like. Preferred examples of the CO₂R moiety are a loweralkoxycarbonyl group, a lower alkenyloxycarbonyl group, a loweralkynyloxycarbonyl group, an aryl lower alkoxycarbonyl group (e.g.,benzyloxycarbonyl group), and an aryloxycarbonyl group (e.g.,phenyloxycarbonyl group). Above all, a lower alkoxy-carbonyl group ispreferred and ethoxycarbonyl or methoxy-carbonyl group is mostpreferred.

Examples of the leaving group include a halogen atom (e.g., chlorineatom, bromine atom, iodine atom), an alkanesulfonyloxy group (e.g.,methanesulfonyl group) a halogenoalkanesulfonyloxy group (e.g.,trifluoromethanesulfonyloxy group) and an arylsulfonyloxy group (e.g.,p-toluenesulfonyloxy group). Above all, a halogen atom such as bromineatom and iodine atom, and a halogenoalkanesulfonyloxy group such astrifluoromethanesulfonyloxy group are preferred, and bromine atom andtrifluoromethanesulfonyloxy group are most preferred.

The coupling reaction can be carried out under the conditions of Suzukicoupling reaction, making reference to, for example, (a) Synth. Commun.11: 513 (1981); (b) Pure and Appl. Chem. 57: 1749 (1985); (c) Chem. Rev.95: 2457 (1995); (d) J. Org. Chem. 57: 379 (1992); (e) Acta ChemicaScandinavica 47: 221 (1993); (f) J. Org. Chem., 60: 1060 (1995); and (g)Organic Letters, 3: 3049 (2001).

Examples of the catalyst include those used in the Suzuki couplingreaction (e.g., palladium or nickel catalysts). Palladium catalysts suchas palladium (II) catalysts (e.g., palladium acetate, palladiumchloride, dichlorobis(triphenylphosphine)palladium, etc.) and palladium(0) catalysts (palladium tetrakistriphenylphosphine, etc.) can be usedconveniently. The palladium catalyst can be used in a catalytic amount,specifically in amount of 1-10 mole %, preferably 4-6 mole %.

In case that a palladium (II) catalyst which does not have ligands inits molecule, such as palladium acetate or palladium chloride, is used,it is preferable to add a phosphine or a phosphite to the reaction inorder to facilitate the reaction. Examples of the phosphine includetritolylphosphine, triphenylphosphine, trimethylphosphine,triethylphosphine, etc., and examples of the phosphite includetrimethylphosphite, triethylphosphite, tri(n-butyl)phosphitge, etc. Thephosphine or phosphite can be used in amount of 3-50 mole %, preferably10-30 mole %.

Among the palladium catalysts above, palladium acetate and palladiumchloride are stable and thus preferred, and palladium acetate is morepreferred.

Examples of the base that can be used in the reaction includeconventional bases, for example, inorganic bases such as alkali metalcarbonates (sodium carbonate, potassium carbonate, etc.), alkali metalhydrogen carbonates (sodium hydrogen carbonate, potassium hydrogencarbonate, etc.), alkali metal hydroxides (sodium hydroxide, potassiumhydroxide, etc.), and organic bases such as alkylamines(diisopropylamine, triethylamine, diisopropylethylamine, etc.),pyridines (pyridine, dimethylaminopyridine, etc.), and cyclic amines(1,8-diazabicyclo[5.4.0]undec-7-ene, 1,4-diazabicyclo[2.2.2]octane,morpholine, 4-methylmorpholine, etc.). Among them, alkylamines(especially diisopropylamine) and cyclic amines (especially morpholine)are preferred. The base can be conveniently used in an amount of 1.0-3.0mole equivalents, preferably 1.5-2 mole equivalents.

Any solvents are available so long as the coupling reaction is notadversely affected, and, for example, an organic solvent, water or amixed solvent thereof can be used. Examples of preferred organic solventinclude amides (e.g., dimethylformamide and N-methylpyrrolidone),aromatic hydrocarbons (e.g., benzene and toluene), ethers (e.g., diethylether, tetrahydrofuran, dimethoxyethane and dioxane), alcohols (e.g.,methanol and ethanol), and a mixture thereof. Above all, amidesespecially N-methylpyrrolidone is preferred.

The reaction can be carried out at a temperature of −20° C. to 180° C.,more preferably at room temperature to 120° C., most preferably at 50°C. to 100° C.

The deprotection method for removing the protecting group from theprotected amino group is selected depending on the type of protectinggroup to be removed. For example, the deprotection can be conducted by amethod selected from the followings:

-   (1) reduction with a catalyst (e.g., palladium on carbon) under a    hydrogen atmosphere;-   (2) treatment with an acid such as hydrogen chloride,    trifluoroacetic acid, p-toluenesulfonic acid, etc.;-   (3) treatment with an amine such as piperidine, etc.; and-   (4) treatment with a catalyst such as Wilkinson's catalyst, etc., at    a temperature of under cooling to under heating in an appropriate    solvent selected from organic solvents (e.g., halogenated    hydrocarbons such as dichloromethane, chloroform, etc., ethers such    as dioxane, tetrahydrofuran, etc., alcohols such as methanol,    ethanol, etc., and acetonitrile, etc.), water and a mixed solvent    thereof, or without solvent. For example, when the protecting group    is t-butoxycarbonyl group, the deprotection can be conducted by acid    treatment, specifically, by treatment with a hydrochloric acid or    p-toluenesulfonic acid in an appropriate solvent (e.g., esters such    as ethyl acetate, etc., or alcohols such as ethanol, etc.) at a    temperature of room temperature to under heating, preferably from at    50° C. to the boiling point of the solvent.    (2) STEP 2:

The condensation of the compound (III) or a salt thereof with thecompound (IV) or a salt thereof can be carried out using a condensingagent in the presence or absence of a base in an appropriate solvent orwithout solvent.

The condensing agent can be selected from conventional condensing agentsfor peptide synthesis, for example,chlorobis(2-oxo-3-oxazolidinyl)phosphine(BOP-Cl),benzotriazol-1-yloxytris(dimethylamino)phosphonium hexafluorophosphate(BOP reagent), dicyclohexylcarbodiimide,1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) orcarbonyldiimidazole. It is preferred to use an activator such as1-hydroxybenzotriazole (HOBT) in association with a condensing agent.

Examples of the base that can be used in the reaction includeconventional bases, for example, organic bases such as alkylamines(triethylamine, diisopropylethylamine, etc.), pyridines (pyridine,dimethylaminopyridine, etc.) and cyclic amines(1,8-diazabicyclo[5.4.0]undec-7-ene, 4-methylmorpholine, etc.), andinorganic bases such as alkali metal hydroxides (sodium hydroxide,potassium hydroxide, etc.), alkali metal carbonates (sodium carbonate,potassium carbonate, etc.) and alkali metal hydrogen carbonates (sodiumhydrogen carbonate, potassium hydrogen carbonate, etc.).

Any solvents are available so long as the condensation reaction is notadversely affected, and, for example, esters (methyl acetate, ethylacetate, etc.), halogenated hydrocarbons (dichloromethane, chloroform,dichloroethane, carbon tetrachloride, etc.), aromatic hydrocarbons(benzene and toluene), ethers (diethyl ether, tetrahydrofuran, dioxane,etc.), ketones (acetone, methyl ethyl ketone, etc.), amides(dimethylformamide, N-methylpyrrolidone, etc.), or a mixed solventthereof can be conveniently used.

The reaction can be carried out at a temperature of −50° C. to 50° C.,preferably at 0° C. to room temperature.

The condensation reaction of a reactive derivative of compound (III)with a compound (II) or a salt thereof can be carried out in thepresence or absence of a base in an appropriate solvent or withoutsolvent.

Examples of the reactive derivative include an acid halide (acidchloride, etc.), a reactive ester (an ester with p-nitrophenol, etc.)and a mixed acid anhydride with other carboxylic acid (a mixed acidanhydride with isobutyric acid, etc.).

Examples of the base that can be used include conventional bases, forexample, organic bases such as alkylamines (triethylamine,diisopropylethylamine, etc.), pyridines (pyridine,dimethylaminopyridine, etc.) and cyclic amines(1,8-diazabicyclo[5.4.0]undec-7-ene, 4-methylmorpholine, etc.), andinorganic bases such as alkali metal hydroxides (sodium hydroxide,potassium hydroxide, etc.), alkali metal carbonates (sodium carbonate,potassium carbonate, etc.) and alkali metal hydrogen carbonates (sodiumhydrogen carbonate, potassium hydrogen carbonate, etc.).

Any solvents are available so long as the condensation reaction is notadversely affected, and, for example, esters (methyl acetate, ethylacetate, etc.), halogenated hydrocarbons (dichloromethane, chloroform,dichloroethane, carbon tetrachloride, etc.), aromatic hydrocarbons(benzene, toluene, etc.), ethers (diethyl ether, tetrahydrofuran,dioxane, etc.), ketones (acetone, methyl ethyl ketone, etc.), amides(dimethylformamide, N-methylpyrrolidone, etc.), water, or a mixedsolvent thereof can be conveniently used.

It is more preferable to carry out the present condensation reactionunder the reaction conditions for so-called Schotten-Baumann reactionamong the above-mentioned reaction conditions. For example, the reactionis preferably carried out using an acid halide (preferably, acidchloride) of compound (III) in the presence of an inorganic base such asalkali metal hydrogen carbonate (e.g., sodium hydrogen carbonate,potassium hydrogen carbonate) in a bilayer system of water and anappropriate organic solvent (e.g., ethyl acetate and toluene).

The reaction can be carried out at a temperature of −50° C. to 50° C.,preferably at 0° C. to room temperature.

3. STEP (3)

The deprotection method for removing the protecting group from theprotected carboxyl group of compound (II) is selected depending on thetype of the protecting group to be removed. For example, deprotectioncan be conducted in a conventional manner such as catalytic reduction,acid treatment, hydrolysis, or the like. In particular, when theprotected carboxyl group is an esterified carboxyl group, it can beconverted into the carboxyl group by hydrolysis.

Although the hydrolysis may vary depending on the kind of the estergroup to be removed, it can be conducted with an acid or a base in asuitable solvent or without solvent. Examples of the acid that can beused include inorganic acids such as hydrochloric acid, nitric acid,sulfuric acid, etc., and organic acids such as trifluoroacetic acid,p-toluenesulfonic acid, etc. Examples of the base that can be used inthe reaction include inorganic bases such as alkali metal hydroxides(e.g., lithium hydroxide and sodium hydroxide), alkali metal carbonates(e.g., sodium carbonate and potassium carbonate), alkali metal hydrogencarbonates (e.g., sodium hydrogen carbonate and potassium hydrogencarbonate), alkali earth metal hydroxides (e.g., calcium hydroxide),etc. and organic bases such as alkali metal alkoxides (e.g., sodiummethoxide, sodium ethoxide, potassium methoxide and potassium ethoxide),alkali earth metal alkoxides (e.g., calcium methoxide and calciumethoxide), etc. Alkali metal hydroxides such as lithium hydroxide andsodium hydroxide are preferred. Any solvents are available so long asthe hydrolysis is not adversely affected, and, for example, water, anorganic solvent or a mixed solvent thereof can be used. Examples of theorganic solvent include ethers (e.g., diethyl ether, dioxane andtetrahydrofuran), alcohols (e.g., methanol, ethanol, propanol andethyleneglycol), acetonitrile and ketones (e.g., acetone and methylethyl ketone). Above all, alcohols such as methanol and ethanol andethers such as dioxane and tetrahydrofuran are preferred.

The reaction can be carried out at a temperature of under cooling to theboiling point of the solvent, preferably at room temperature to 50° C.

The pharmaceutically acceptable salts of the compound (I) include a saltwith an inorganic base (e.g., an alkali metal salt such as a sodiumsalt, a potassium salt, etc.; an alkali earth metal salt such asmagnesium salt, calcium salt, etc.) and a salt with an organic base(e.g., ammonium salt; a lower alkyl ammonium salt such as methylammoniumsalt, ethylammonium salt, etc.; pyridinium salt; or a salt with a basicamino acid such as a salt with lysine, etc.). The compound (I) can beconverted into a pharmaceutically acceptable salt in a conventionalmanner.

Examples of the compounds that are preferably used for carrying out thepresent process include those wherein X¹ is chlorine atom or fluorineatom, X² is chlorine atom or fluorine atom, Y is a lower alkyl grouphaving 1 to 4 carbon atoms and CO₂R is a lower alkoxycarbonyl group.

More preferred compounds for carrying out the present process includethose wherein Q is group of the formula —CH₂—, Y is methyl group, ethylgroup or n-propyl group, and CO₂R is methqxycarbonyl group,ethoxycarbonyl group or t-butoxycarbonyl group.

Still more preferred compounds for carrying out the present processinclude those wherein X¹ is fluorine atom, Y is methyl group or ethylgroup, and CO₂R is methoxycarbonyl group or ethoxycarbonyl group.

Especially preferred compounds for carrying out the present processinclude those wherein X¹ is fluorine atom, X² is fluorine atom, Y isethyl group, and CO₂R is ethoxycarbonyl group, or those wherein X¹ isfluorine atom, X² is chlorine atom, Y is ethyl group, and CO₂R ismethoxycarbonyl group or ethoxycarbonyl group.

The most preferred compound that can be produced according to thepresent process is(αS)-α-[(2,6-difluorobenzoyl)amino]-4′-ethoxymethyl-2′,6′-dimethoxy(1,1′-biphenyl)-4-propionicacid.

The compound (I) or a pharmaceutically acceptable salt thereof, which isan objective compound of the present process, is a novel compound. Thecompound (I) or a pharmaceutically acceptable salt thereof not onlyshows potent inhibitory activity against α₄ integrin-mediated celladhesion but also shows excellent bioavailability after oraladministration which reflects overall improvement in metabolicstability, plasma protein binding and aqueous solubility. Accordingly,the compound (I) is useful in treatment of diseases caused by α₄integrin-mediated cell adhesion, including rheumatoid arthritis, atopicdermatitis, psoriasis, asthma, bronchitis, multiple sclerosis,inflammatory bowel disease, experimental autoimmune encephalomyelitis,and the like.

Further, a compound of the formula (IV):

wherein the symbols are the same as defined above, or a salt thereof isnovel and useful as an intermediate for the process of the presentinvention. A compound of the formula (IV) wherein Q is a group of theformula —CH₂—, Y is ethyl group, CO₂R is ethoxycarbonyl group, namely,ethylα-amino-4′-ethoxymethyl-2′,6′-dimethoxy(1,1′-biphenyl)-4-propionate or asalt thereof, and especially, in the S-form, is preferred for theprocess of the present invention.

Besides, another starting compound of the formula (V):

wherein the symbols are the same as defined above is also novel anduseful in the reactions for the present process. A compound (V) whereinQ is a group of the formula —CH₂— and Y is ethyl group is particularlyuseful in the present invention.

The compound (V) can be prepared according to the following method.

First, the hydroxyl group of a compound of the formula (VII):

wherein the symbol is the same as defined above, or that of a compoundof the formula (VIII):

wherein the symbol is the same as defined above is alkylated. Theresultant compound is then subjected to lithiation followed by reactionwith a tri-lower alkyl borate. The resultant compound is hydrolyzed togive the compound (V).

The alkylation can be carried out using an alkylating agent in asuitable solvent in the presence of a base. Examples of the alkylatingagent include di-lower alkyl sulfates such as dimethyl sulfate, diethylsulfate, etc., and lower alkyl halides such as methyl iodide, ethyliodide, etc. Examples of the base include inorganic bases such as alkalimetal hydroxides (sodium hydroxide, potassium hydroxide, etc.), alkalimetal carbonates (sodium carbonate, potassium carbonate, etc.) andalkali metal hydrogen carbonates (sodium hydrogen carbonate, etc.), andorganic bases such as alkylamines (triethylamine, diisopropylethylamine,etc.) and pyridines (pyridine, dimethylaminopyridine, etc.). Anysolvents are available so long as the reaction is not adverselyaffected, and, for example, water, acetonitrile, amides(N,N-dimethylformamide, etc.), ethers (tetrahydrofuran, etc.), aromatichydrocarbons (toluene, etc.), halogenated hydrocarbons (dichloromethane,etc.), or a mixed solvent thereof can be used. The reaction can becarried out in a suitable solvent at a temperature of about 0° C. toabout 100° C., preferably at room temperature to about 70° C. Thepresent reaction can be expedited by adding a catalytic amount of aphase-transfer catalyst such as triethylammonium benzyl chloride.

The lithiation and the reaction with tri-lower alkyl borate can becarried out by subjecting a compound to lithiation with an alkyl lithiumfollowing by the reaction with a tri-lower alkyl borate in a suitablesolvent. Preferred alkyl lithium may be methyl lithium, n-butyl lithium,t-butyl lithium, and the like. Preferred tri-lower alkyl borate may betrimethyl borate, triethyl borate, and the like. Any solvents areavailable so long as the reaction is not adversely affected, and, forexample, organic solvents such as ethers (diethyl ether,tetrahydrofuran, etc.) and a mixed solvent thereof are preferred. Thepresent reaction can be carried out at a temperature of under cooling(e.g., −100° C.) to room temperature.

The hydrolysis can be carried out with an acid in a suitable solvent.Examples of the acid include organic acids such as acetic acid,trifluoroacetic acid and citric acid and inorganic acids such ashydrochloric acid, sulfuric acid and nitric acid. Any solvents areavailable so long as the reaction is not adversely affected and, forexample, organic solvents such as ethers (diethyl ether,tetrahydrofuran, etc.) and a mixed solvent thereof can be used.

Ethyl (αS)-α-[[(1,1-dimethylethoxy)carbonyl]amino]-4-hydroxybenzenepropionate and ethyl(αS)-α-[[1,1-dimethylethoxy)carbonyl]amino]-4-(trifluoromethanesulfonyloxy)benzenepropionate are described in J. Med. Chem., 33: 1620 (1990) andJP-A-7-157472, respectively. 4-Bromo-3,5-dimethoxybenzyl alcohol isdescribed in, for example, J. Med. Chem., 20: 299 (1977), and can alsobe prepared according to the following process.

Firstly, 4-bromo-3,5-dihydroxybenzoic acid is methylated to give methyl4-bromo-3,5-dimethoxybenzoate, which is then reduced to yield4-bromo-3,5-dimethoxy benzyl alcohol. The methylation can be carried outby reacting with dimethyl sulfate in the presence of a base in asuitable solvent (e.g., ethyl acetate). The reduction can be carried outby reacting with an reducing agent (e.g., lithium alminium hydride,sodium borohydride and calcium borohydride) in a suitable solvent (e.g.,tetrahydrofuran).

Throughout the present description and claims, the term “lower alkyl”means straight- or branched-chain alkyl having 1 to 6 carbon atoms,preferably 1 to 4 carbon atoms, for example, methyl, ethyl, propyl,isopropyl, butyl and the like. The term “lower alkoxycarbonyl” meansstraight- or branched-chain alkoxycarbonyl having 2 to 7 carbon atoms,preferably 2 to 5 carbon atoms, for example, methoxycarbonyl,ethoxycarbonyl, propoxycarbonyl, isopropoxycarbonyl, butoxycarbonyl andthe like. The term “lower alkenyl” means straight- or branched-chainalkenyl having 2 to 7 carbon atoms, preferably 2 to 4 carbon atoms, forexample, vinyl, allyl, isopropenyl and the like. The term “loweralkenyloxycarbonyl” means straight- or branched-chain alkenyloxycarbonylhaving 2 to 7 carbon atoms, preferably 2 to 4 carbon atoms, for example,vinyloxycarbonyl, allyloxycarbonyl, isopropenyloxycarbonyl and the like.The term “lower alkynyl” means straight- or branched-chain alkynylhaving 2 to 7 carbon atoms, preferably 2 to 4 carbon atoms, for example,ethynyl, 2-propynyl and the like. The term “lower alkynyloxycarbonyl”means straight- or branched-chain alkynyloxycarbonyl having 2 to 7carbon atoms, preferably 2 to 4 carbon atoms, for example,ethynyloxycarbonyl, 2-propynyloxycarbonyl and the like. Further,“t-butoxy” means 1,1-dimethylethoxy.

EXAMPLES

The following Examples are provided to further illustrate the process ofpreparation according to the present invention. In the followingexamples, some compounds may be referred to by different compound namedepending on the nomenclature, as illustrated below.

-   Ethyl    (αS)-α-amino-4′-ethoxymethyl-2′,6′-dimethoxy(1,1′-biphenyl)-4-propionate-   Another name: ethyl    (2S)-2-amino-3-[4-(4-ethoxymethyl-2,6-dimethoxyphenyl)phenyl]propanoate-   Ethyl    (αS)-[[1,1-dimethylethoxy]carbonyl]amino]-4′-ethoxymethyl-2′,6′-dimethoxy(1,1′-biphenyl)-4-propionate-   Another name 1: ethyl    (2S)-2-[(t-butoxycarbonyl)-amino]-3-[4-(4-ethoxymethyl-2,6-dimethoxyphenyl)-phenyl]propanoate-   Another name 2: Ethyl    N-(t-butoxycarbonyl)-4-(4-ethoxymethyl-2,6-dimethoxyphenyl)-L-phenylalanine-   Ethyl    (αS)-α-[(2,6-difluorobenzoyl)amino]-4′-ethoxymethyl-2′,6′-dimethoxy(1,1′-biphenyl)-4-propionate-   Another name 1: Ethyl    (2S)-2-[(2,6-difluorobenzoyl)amino]-3-[4-(4-ethoxymethyl-2,6-dimethoxyphenyl)phenyl]propanoate-   Another name 2: Ethyl    N-(2,6-difluorobenzoyl)-4-(4-ethoxymethyl-2,6-dimethoxyphenyl)-L-phenylalanine-   (αS)-α-[(2,6-Difluorobenzoyl)amino]-4′-ethoxymethyl-2′,6′-dimethoxy(1,1′-biphenyl)-4-propionic    acid-   Another name 1:    (2S)-2-[(2,6-difluorobenzoyl)amino]-3-[4-(4-ethoxymethyl-2,6-dimethoxyphenyl)phenyl]propanoic    acid-   Another name 2:    N-(2,6-difluorobenzoyl)-4-(4-ethoxymethyl-2,6-dimethoxyphenyl)-L-phenylalanine

Example 1

(1) Under nitrogen atmosphere, pyridine(130.3 g) andtrifluoromethanesulfonic anhydride (170.4 g) were added dropwise to asolution of ethyl(αS)-α-[[(1,1-dimethylethoxy)carbonyl]amino]-4-hydroxybenzenepropionate(170.0 g) in dichloromethane (1.7 L) at 10° C. or below. After stirringfor 1 hour at the same temperature, water (850 ml) was added dropwise tothe mixture and the mixture was stirred for 2 hours at the sametemperature. The organic layer was washed with 10% aqueous citric acidsolution and aqueous saturated sodium hydrogen carbonate solution, anddried over magnesium sulfate. The solvent was removed in vacuo to yieldethyl(αS)-α-[[(1,1-dimethylethoxy)carbonyl]amino]-4-(trifluoromethanesulfonyloxy)benzenepropionate(242.5 g) as oil.

MS (m/z): 441 (M⁺)

(2) Under nitrogen atmosphere, to a mixture of ethyl(αS)-α-[[(1,1-dimethylethoxy)carbonyl]amino]-4-(trifluoromethanesulfonyloxy)benzenepropionate(66.2 g), 4-ethoxymethyl-2,6-dimethoxyphenylboric acid (54.0 g),triphenylphosphine (9.83 g) and N-methylpyrrolidone (330 ml) were addedpalladium acetate (1.68 g) and diisopropylamine (24.9 g), and themixture was heated at 90° C. After stirring for 1 hour at the sametemperature, the mixture was cooled and toluene and water were added.The organic layers were washed with 10% aqueous citric acid solution andsaturated aqueous NaCl solution and dried over magnesium sulfate. Thesolvent was removed in vacuo to yield ethyl(αS)-α-[[(1,1-dimethylethoxy)carbonyl]amino]-4′-ethoxymethyl-2′,6′-dimethoxy(1,1′-biphenyl)-4-propionate(90.1 g) as oil.

The product was dissolved in ethanol (330 ml), and after addition ofp-toluenesulfonic acid monohydrate (28.5 g), the mixture was stirred for2 hours at 75° C. After cooling to room temperature, the mixture wasfiltrated over charcoal and the filtrate was concentrated under reducedpressure. The residue was dissolved in ethyl acetate with heating. Aftercooling, the crystalline precipitates were collected by filtration anddried to yield ethyl(αS)-α-amino-4′-ethoxymethyl-2′,6′-dimethoxy(1,1′-biphenyl)-4-propionatep-toluenesulfonate (63.4 g).

MS (m/z): 387 (M⁺-p-toluenesulfonic acid), M.p. 127-129° C.

(3) To a mixture of ethyl(αS)-α-amino-4′-ethoxymethyl-2′,6′-dimethoxy(1,1′-biphenyl)-4-propionatep-toluenesulfonate (29.0 g), sodium hydrogen carbonate (15.2 g), water(290 ml) and ethyl acetate (290 ml) was added dropwise2,6-difluorobenzoyl chloride (9.6 g) at 15° C. or below and the mixturewas stirred for 30 minutes at the same temperature. The ethyl acetatelayer was washed with saturated aqueous NaCl solution and dried overmagnesium sulfate. The solvent was removed in vacuo. The residue wasrecrystallized from isopropanol-water to yield ethyl(αS)-α-[(2,6-difluorobenzoyl)amino]-4′-ethoxymethyl-2′,6′-dimethoxy(1,1′-biphenyl)-4-propionate(26.4 g).

MS (m/z): 527 (M⁺), M.p. 87-89° C.

(4) To a solution of sodium hydroxide (2.9 g) in water-tetrahydrofuran(317 ml-159 ml) was added ethyl(αS)-α-[(2,6-difluorobenzoyl)amino]-4′-ethoxymethyl-2′,6′-dimethoxy(1,1′-biphenyl)-4-propionate(31.7 g) at 15° C. and the mixture was stirred for 4 hours at the sametemperature. After neutralizing with 1N HCl, the organic solvent wasremoved in vacuo. The aqueous layer was cooled, the crystallineprecipitates were collected by filtration and recrystallized fromethanol-water to yield(αS)-α-[(2,6-difluorobenzoyl)amino]-4′-ethoxymethyl-2′,6′-dimethoxy(1,1′-biphenyl)-4-propionicacid (28.8 g).

MS (m/z): 499 (M⁺), M.p. 154-155° C.

Example 2

(1) Under nitrogen atmosphere, a mixture of ethyl(αS)-α-[[(1,1-dimethylethoxy)carbonyl]amino]-4-bromobenzene propanoate(11.17 g), 4-ethoxymethyl-2,6-dimethoxyphenylboronic acid (10.80 g),palladium acetate (0.34 g), triphenylphosphine (1.57 g), anhydrouspotassium carbonate (12.44 g), N-methylpyrrolidone (56 ml) and water (11ml) was stirred for 50 minutes at 80° C. After completion of thereaction, the mixture was cooled to room temperature and extracted withethyl acetate and water. The organic layer was washed with 10% aqueouscitric acid solution and saturated aqueous NaCl solution, dried overmagnesium sulfate and filtrated. The filtrate was concentrated underreduced pressure to yield ethyl(αS)-α-[[(1,1-dimethylethoxy)carbonyl]amino]-4′-ethoxymethyl-2′,6′-dimethoxy(1,1′-biphenyl)-4-propionate(20.4 g) as oil.

The product was dissolved in ethanol (100 ml), and after addition ofp-toluenesulfonic acid monohydrate (5.7 g), the mixture was stirred for1.5 hours at 75° C. After cooling, the mixture was filtrated overcharcoal and the filtrate was concentrated under reduced pressure. Theresidue was suspended in toluene with heating. After cooling, thecrystalline precipitates were collected by filtration and dried to yieldethyl(αS)-α-amino-4′-ethoxymethyl-2′,6′-dimethoxy(1,1′-biphenyl)-4-propionatep-toluenesulfonate (13.80 g).

(2) The compound obtained in the above step (1) was treated in the samemanner as described in Example 1 (2) to (4) to yield(αS)-α-[(2,6-difluorobenzoyl)amino]-4′-ethoxymethyl-2′,6′-dimethoxy(1,1′-biphenyl)-4-propionicacid. The physicochemical data were the same as that obtained in Example1.

Example 3

To a solution of ethyl(αS)-α-[(2,6-difluorobenzoyl)amino]-4′-ethoxymethyl-2′,6′-dimethoxy(1,1′-biphenyl)-4-propionate(500 mg) in water (12.6 ml) and dioxane (50 ml) was added hydrochloricacid (12.4 g) and the mixture was stirred for 60 hours at 60° C. Theorganic solvent was removed in vacuo and the aqueous layer was cooled.The crystalline precipitates were collected by filtration andrecrystallized from ethanol-water to yield(αS)-α-[(2,6-difluorobenzoyl)amino]-4′-ethoxymethyl-2′,6′-dimethoxy(1,1′-biphenyl)-4-propionicacid (426 mg). The physicochemical data were the same as that obtainedin Example 1.

Reference Example 1

(1) To a mixture of 4-bromo-3,5-dimethoxybenzylalcohol (44.5 g),triethylammonium benzyl chloride (2.05 g) and 20% aqueous sodiumhydroxide solution (288 g) was added diethyl sulfate (41.7 g) underice-cooling, and the mixture was stirred overnight at 25-30° C. Afterstirring for 1 hour at 70° C., the mixture was cooled and extracted withtoluene. The toluene layer was washed with water and saturated aqueousNaCl solution and dried over magnesium sulfate. The solvent was removedin vacuo to yield 4-bromo-3,5-dimethoxybenzyl ethyl ether (49.5 g) ascolorless oil.

MS (m/z): 276 (M⁺+2), 274 (M⁺)

(2) Under nitrogen atmosphere, to a solution of4-bromo-3,5-dimethoxybenzyl ethyl ether (440.0 g) in tetrahydrofuran(4.0 L) was added dropwise n-butyl lithium (1.6 M n-hexane solution, 1.1L) at −60° C. After stirring for 15 minutes at the same temperature,trimethyl borate (249.3 g) was added. The temperature of the mixture wasgradually elevated, followed by stirring for 1 hour under ice-cooling.To the mixture was added dropwise 10% aqueous sulfuric acid solution(835 g). The mixture was extracted with ethyl acetate and the organiclayer was washed with water and saturated aqueous NaCl solution. Afterdrying over magnesium sulfate, the solvent was removed in vacuo. Theresidue was dissolved in isopropyl ether with heating and cooled. Thecrystalline precipitates were collected by filtration and dried to yield4-ethyoxymethyl-2,6-dimetoxyphenylboronic acid (312.9 g).

M.p. 59-61° C.

Reference Example 2

(1) To a suspension of 4-bromo-3,5-dihydroxybenzoic acid (95.0 kg) inethyl acetate (950 L) were added anhydrous potassium carbonate (270.8kg) and dimethyl sulfate (174.7 kg). The mixture was heated at 50-80° C.for about 4 hours and partitioned by adding water. The organic layer waswashed with water and saturated aqueous NaCl solution and concentratedunder reduced pressure. The residue was suspended into methanol, stirredunder heating and cooled. The crystalline precipitates were collected byfiltration and dried to yield methyl 4-bromo-3,5-dimethoxybenzoate (98.8kg) as pale yellow crystals.

MS (m/z): 277 (M⁺+2), 275 (M⁺), M.p. 120-122° C.

(2) To a solution of calcium chloride (46.5 kg) in ethanol (336 L) wereadded tetrahydrofuran (672 L) and methyl 4-bromo-3,5-dimethoxybenzoate(96.0 kg) to obtain a suspension. To the suspension was added sodiumborohydride (31.7 kg) by portions at room temperature, and the mixturewas stirred for about 9 hours at temperature of room temperature to 45°C. The reaction mixture was added dropwise to aqueous HCl solution andstirred for about 16 hours at room temperature. Organic solvent wasremoved in vacuo, and water (1440 L) was added to the residue andstirred for 1 hour at 50° C. After cooling, the crystalline precipitateswere collected by filtration and dried to yield4-bromo-3,5-dimethoxybenzyl alcohol (83.3 kg) as colorless crystals.

MS (m/z): 249 (M⁺+2), 247 (M⁺), M.p. 100-102° C.

INDUSTRIAL APPLICABILITY

The process for preparation of the present invention makes it possibleto afford a compound of the formula (I) or a pharmaceutically acceptablesalt thereof with high-purity, in a high yield and inexpensively, and,therefore, the process of the present invention is industrially veryuseful.

1. A process for preparing a phenylalanine derivative of the formula(I):

wherein X¹ is a halogen atom, X² is a halogen atom, q is a group of theformula —CH₂— or —(CH₂)₂— and Y is a lower alkyl group, or apharmaceutically acceptable salt thereof, which comprises condensing acompound of the formula (IV):

wherein CO₂R is a protected carboxyl group and the other symbols are thesame as defined above, or a salt thereof, with a compound of the formula(III):

wherein the symbols are the same as defined above, a salt or a reactivederivative thereof to yield a compound of the formula (II):

wherein the symbols are the same as defined above, and removing theprotecting group from the protected carboxyl group of the compound (II),and if necessary, followed by converting the resulting compound into apharmaceutically acceptable salt.
 2. A process for preparing aphenylalanine derivative of the formula (I):

wherein X¹ is a halogen atom, X² is a halogen atom, Q is a group of theformula —CH₂— or —(CH₂)₂— and Y is a lower alkyl group, or apharmaceutically acceptable salt thereof, which comprises coupling acompound of the formula (VI):

wherein Z is a leaving group, R¹NH is a protected amino group and CO₂Ris a protected carboxyl group with a compound of the formula (V):

wherein the symbols are the same as defined above, removing theprotecting group from the protected amino group, and if necessary,converting the resulting compound into a salt to yield a compound of theformula (IV):

wherein the symbols are the same as defined above, or a salt thereof,and condensing the compound (IV) or a salt thereof with a compound ofthe formula (III):

wherein the symbols are the same as defined above, a salt or a reactivederivative thereof to yield a compound of the formula (II):

wherein the symbols are the same as defined above, removing theprotecting group from the protected carboxyl group of the compound (II),and if necessary, followed by converting the resulting compound into apharmaceutically acceptable salt.
 3. The process according to claim 1 or2, wherein X¹ is chlorine atom or fluorine atom, X² is chlorine atom orfluorine atom, Y is a C₁₋₄ alkyl group and CO₂R is a loweralkoxycarbonyl group.
 4. The process according to claim 3, wherein Q isa group of the formula —CH₂—, Y is methyl group, ethyl group or n-propylgroup, and CO₂R is methoxycarbonyl group, ethoxycarbonyl group ort-butoxycarbonyl group.
 5. The process according to claim 4, wherein X¹is fluorine atom, Y is methyl group or ethyl group, and CO₂R ismethoxycarbonyl group or ethoxycarbonyl group.
 6. The process accordingto claim 4, wherein X¹ is fluorine atom, X² is fluorine atom, Y is ethylgroup, and CO₂R is ethoxycarbonyl group.
 7. The process according toclaim 4, wherein X¹ is fluorine atom, X² is chlorine atom, Y is ethylgroup, and CO₂R is methoxycarbonyl group or ethoxycarbonyl group.
 8. Acompound of the formula (IV):

wherein Q is a group of the formula —CH₂— or —(CH₂)₂—, Y is a loweralkyl group and CO₂R is a protected carboxyl group, or a salt thereof.9. The compound according to claim 8, wherein Q is a group of theformula —CH₂—, Y is ethyl group and CO₂R is ethoxycarbonyl group.
 10. Aprocess for preparing a compound of the formula (IV):

wherein Q is a group of the formula —CH₂— or —(CH₂)₂—, Y is a loweralkyl group and CO₂R is a protected carboxyl group, or a salt thereof,which comprises coupling a compound of the formula (VI):

wherein Z is a leaving group, R¹NH is a protected amino group and CO₂Ris the same as defined above with a compound of the formula (V):

wherein the symbols are the same as defined above, removing the aminoprotecting group, and if necessary, followed by converting the resultingcompound into a salt.
 11. The process according to claim 10, wherein Qis a group of the formula —CH₂—, Y is ethyl group and CO₂R isethoxycarbonyl group.
 12. A compound of the formula (V):

wherein Q is a group of the formula —CH₂— or —(CH₂)₂— and Y is a loweralkyl group.
 13. The compound according to claim 12, wherein Q is agroup of the formula —CH₂— and Y is ethyl group.